1. Field of the Invention
The apparatus of the present invention relates generally to material transfer devices, and more specifically to an apparatus for transferring silicon wafers to and from a plurality of work stations.
2. Description of the Prior Art
The transfer of delicate silicon wafers or the like between a plurality of work stations or locations in the manufacture of semiconductor devices presents unique handling problems. The silicon wafers are very delicate and have highly polished surfaces. When the wafers are abruptly moved, they tend to slide. This sliding action can cause the silicon wafers to abrade or alternatively can cause damage to their edges if they collide.
There are numerous devices described in the prior art for transferring silicon wafers. For example:
U.S. Pat. No. 3,823,836 discloses an apparatus which includes a supply carrier with a plurality of ledges to hold the silicon wafers and a withdrawal device having a vacuum chuck. The vacuum chuck is attached to an elevator which raises and lowers the chuck. A horizontal transfer arm coupled to the vacuum chuck is used to transfer the silicon wafer from the supply carrier to a desired work station.
U.S. Pat. No. 3,730,595 discloses a wafer transfer handling apparatus having an indexable carrier for transferring wafers to and from work stations. Wafers enter and leave the wafer carrier on an air slide with the aid of a wafer ejector acceptor arm having directional air jets. The wafer ejector acceptor arm controls the driving of the wafers into or out of the carrier from or on to the air slide which moves the wafers to or from a work station.
U S. Pat. No. 4,062,463, 3,874,525 and 4,208,159 also disclose wafer transfer devices which include either pneumatic components or gripping devices for handling the wafers.
The above described devices of the prior art utilize relatively complex and costly pneumatic components or utilize undesirable gripping devices which may do damage to the delicate wafers. Moreover, the above described devices tend to be limited to the transfer of silicon wafers between fixed locations which are difficult to change.
Accordingly, there is a need for a simple and reliable transfer device that will not damage the object and that is capable of transferring objects between a plurality of locations disposed in various axial and radial planes.